DUBAI (Reuters) - Iran's supreme leader on Saturday backed President Hassan Rouhani's suggestion that Iran may block Gulf oil exports if its own exports are stopped, according to his official website.

"(Ayatollah Ali Khamenei) said remarks by the president ... that 'if Iran's oil is not exported, no regional country's oil will be exported,' were important remarks that reflect the policy and the approach of (Iran's) system," Khamenei's website said.

Rouhani's apparent threat earlier this month to disrupt oil shipments from neighbouring countries came in reaction to looming U.S. sanctions and efforts by Washington to force all countries to stop buying Iranian oil.

Iranian officials have in the past threatened to block the Strait of Hormuz, a major oil shipping route, in retaliation for any hostile U.S. action.

Khamenei used a speech to foreign ministry officials to reject any renewed talks with the United States after President Donald Trump’s decision to withdraw from a 2015 international deal over Iran's nuclear programme.

"The word and even the signature of the Americans cannot be relied upon, so negotiations with America are of no avail," Khamenei said.

It would be an "obvious mistake" to negotiate with the United States as Washington was unreliable, Khamenei added according to his website.